New worries about canine flu: Should you vaccinate your dog?

Published 4:00 am, Wednesday, September 29, 2010

Woody, a 5-year-old Flat-coated Retriever owned by Sacramento's Gina Spadafori, almost died of canine influenza virus when he was a puppy.

Woody, a 5-year-old Flat-coated Retriever owned by Sacramento's Gina Spadafori, almost died of canine influenza virus when he was a puppy.

Photo: Gina Spadafori

New worries about canine flu: Should you vaccinate your dog?

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A virus that first started making dogs sick in 2004 may turn out to be more dangerous than originally thought.

The virus, H3N8, dubbed "canine influenza virus" (CIV), was identified as the cause of respiratory disease in racing greyhounds in Florida six years ago.

It was of huge interest to epidemiologists and virologists at the time, because it was the first influenza virus known to affect dogs. In terms of day-to-day veterinary care of pet dogs, however, it was thought to be just one more bug that could make dogs cough.

Dog owners have long known that at the dog park, in dog daycare, at the vet's office, or just during a friendly sniff-fest as dogs pass each other in the street, germs that cause coughing in canines are spread around fairly easily.

And while these mild respiratory infections sometimes turn into something more serious like pneumonia, such complications are rare. Most cases of canine cough -- also called "kennel cough" or "canine infectious respiratory disease complex" -- are no more dangerous than the common cold in humans.

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When CIV first emerged, researchers at Iowa State Universityestimated that around 10 percent of dogs with CIV symptoms go on to develop pneumonia, and somewhere between one and five percent of those dogs die.

While that was alarming, the fact is, dogs with other forms of canine cough also go on to develop pneumonia in rare instances, and some of those dogs, usually older dogs or those with other health problems, die as well.

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Last month, however, an article in the journal Veterinary Microbiology suggested CIV causes more serious symptoms, and is more easily spread, than other, older bacteria and viruses that cause canine respiratory illness.

The manufacturers of the CIV vaccine, Intervet, issued a press release about the new study. "We know that canine influenza, a new disease for many veterinarians, is often under- or misdiagnosed because clinical signs are similar to other respiratory diseases," said Dr. NallaKannu Lakshmanan, one of the study's authors and a researcher for the company. "Our research further suggests that infected dogs may have serious lung damage that goes undetected because it does not manifest as pneumonia."

In other words, there is evidence that the disease damages even the lungs of dogs who don't develop full-blown pneumonia -- damage sometimes missed because of the lack of obvious symptoms.

Additionally, the virus appears to be more easily transmitted than some of the other causes of canine cough.

"Around 20 percent of them won't have any noticeable symptoms," he said. "But they're probably shedding the virus, which can infect other dogs. And we can't do anything to prevent it because we don't know those dogs are sick."

Moyer works full-time at UPenn and also owns a private veterinary practice in Bethlehem, Pa., but he's also done some speaking on canine influenza at events sponsored by Intervet.

And the company, as the manufacturer of a vaccine for the disease, clearly has an interest in dog owners believing the worst about the virus, so like all cases of "science by press release," what they have to say should be taken with the appropriate amount of sodium chloride.

But it's probably true that the disease is under-diagnosed, and that it can be somewhat more serious than many of the other causes of canine respiratory disease, all of which have been around for a long time.

Emerging diseases are often more deadly than established ones, because the species hasn't yet adapted to resist or tolerate the pathogen.

Moreover, we don't know much about new diseases by virtue of the fact that they're just that: new. The first few years after a disease emerges, or crosses to a new species, usually involve a period of assumptions followed by corrections of those assumptions.

For example, until recently, conventional wisdom was that CIV is primarily a disease of dogs in group housing situations such as racing kennels, pet boarding facilities and animal shelters, rather than one affecting individually owned pet dogs.

That's true, but given how contagious CIV is, those sources of infection can pose a risk to dogs who have never set foot in a shelter or kennel, and live as pets in our homes.

"The point of exposure is indeed from group housing situations like dog parks, dog daycare, shelters, grooming shops, and veterinary hospitals," Moyer said. "But any dog who is out and about can be exposed by any infected dog with those places in their history."

There is currently only one vaccine for CIV on the market, although Moyer says more may be on the way.

As a vaccine, it's far from perfect. It sometimes doesn't prevent the dog from getting sick but simply makes his symptoms less severe. And even vaccinated dogs who have no symptoms at all can, if infected, still pass the disease along to other dogs.

In addition, not all dogs are equally at risk of getting infected. Stay-at-home dogs, says Moyer, those who don't "interact with an above-average number of dogs and don't rub noses with a lot of other dogs, are at very low risk."

Dogs who congregate with other dogs at places like dog parks and dog daycare are at higher risk, as are the dogs owned by people who foster and care for dogs from shelters and rescue groups.

"Those dogs should be vaccinated," he said.

If the vaccine doesn't protect dogs from infection, may not protect them from illness, and even dogs who are vaccinated and don't get sick can still infect other dogs, is the vaccine really worth giving even to high risk dogs? Moyer says yes.

"The vaccine, at least in experimental work, reduces the period of time dogs shed the virus after infection, from around seven days to about four days," he said. "They also shed a great deal less virus. Because exposure is based on the number of viral particles, vaccinated dogs are much less contagious, at least in experimental situations."

He acknowledges that it would be difficult to do a study of the impact of vaccination on pet dogs outside of a laboratory setting, but he thinks that research on the impact of human flu shots reinforces the canine experimental data.

"When we look at all the things that are done to contain the spread of influenza in people -- things like hand washing and sneezing into the arm," Moyer said, "all of them slow the rate at which the epidemic spreads, but they don't actually reduce the number of people who, over time, become sick in the epidemic.

"The only mitigation effort that actually reduces the number of people who will get sick with the flu is vaccination," he went on. "So in dogs, the vaccine at least has the potential to lower the number of cases of disease, even though there is no evidence of that right now."

Certainly dog owners should discuss the vaccine, and this new research, with their veterinarians.

But perhaps the most important lesson is that we need to take canine respiratory disease seriously. While the treatment for CIV is the same as for other types of infectious coughing in dogs, owners should be even more watchful than usual for any indication a dog is developing pneumonia or a particularly serious case of the disease.

Early signs of canine cough include nasal discharge and cough, including a cough so mild it can be confused with throat clearing. A dog with a fever of more than 104 degrees, lethargy, a green nasal discharge or difficulty breathing is at high risk of developing dangerous complications and needs immediate veterinary attention.

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